"Microsoft likes to say 'It's a journey,'" said Miller of the Redmond, Wash. company's approach to software development. "This looks like it will be a journey, an evolution over the next year or so for Office on the Mac."

Typically Microsoft rolls out a new edition of Office as a complete package, with all-new -- or mostly-new -- applications rather than release bits piecemeal. But the company took a different tack today because of its emphasis on the rent-not-buy subscription model that it's aggressively pushed since January 2013.

Only customers with an active Office 365 subscription can download the refreshed Outlook for OS X. Those subscriptions cost $80 for a four-year deal for college students, between $70 and $100 annually for consumers, and between $99 and $264 per user per year for businesses.

"The new Outlook for Mac is available to Office 365 commercial customers and Office 365 Home, Office 365 Personal and Office 365 University subscribers," wrote the Office team in a blog post announcing Outlook's availability.

Microsoft said that customers could run the new Outlook alongside the existing Outlook bundled as part of Office for Mac 2011, the four-year-old suite that will drop off the firm's support list in January 2016. Computerworld was able to install, activate and use the new Outlook -- which Microsoft has assigned version number 15 -- with only minor disturbances to an already-in-place Outlook 2011.

Those who purchased Office for Mac 2011 as a perpetual license, the familiar pay-once-use-forever model that still dominates sales, will have to wait months to get their hands on the new Outlook. And they'll have to pay for the privilege.

On the same blog, Microsoft said that it would issue a public beta of "the next version of Office for Mac" in the first half of 2015, and ship the final code in the second half of the year. As per Office 365's premise, subscribers will not be charged for the upgrade -- although they must continue to pay the annual or monthly fees. Non-subscribers will have to pony up an unspecified amount for the new suite.

Microsoft did commit to continuing to offer a perpetual-licensed Office for Mac, at least for the 2015 upgrade. "I actually had fears that Microsoft would make the next [Office for Mac] only as non-perpetual," said Miller. "I'm glad they said they will continue [to offer traditional licenses], and glad that they cleared that up today."

Current prices for a non-subscription license to Office for Mac start at $139.99 for a one-license copy of Home & Student, which omits Outlook. The single-license Office & Business, including Outlook, costs $219.99.

Miller called the new Outlook "sparse," adding that the sudden appearance was "a reflection of the new way of building software" at Microsoft, which has pledged to deliver smaller updates at a faster cadence. That tempo has been particularly true for Office 365, which receives a constant stream of fixes, changes and even new features.

But Miller was also a little leery of the approach, at least from what he saw in today's Outlook 15. "Given the sparse features in OneNote and Outlook on the Mac..., I'm kind of afraid of what the rest of the suite will look like," he tweeted Friday.

In an earlier tweet, Miller said, "The rumor was that Office for Mac would have parity with Windows. What I'm seeing right now is far, far away from that."

Although Microsoft did not say that Outlook 15 remains a work in progress, it's certainly possible, perhaps even likely, that with the time remaining before the appearance of an Office for Mac beta, Microsoft will continue to enhance the application -- updating Office 365 users' copies along the way -- so that it is at feature-parity with the Windows version by the time the final code releases a year from now.

Miller said he expects that's how things would work out. "One of the criticisms has been that Outlook has been stagnant, and that the features that have appeared in OWA [Outlook Web Access] are not getting to Outlook," said Miller. "I see [Outlook for Mac] as the start of a more evolutionary approach where the product evolves over time."